Bayesian analysis of multimessenger M-R data with interpolated hybrid EoS

TL;DR

This paper develops a Bayesian framework to analyze neutron star mass-radius data using hybrid equations of state, incorporating observational constraints to infer the properties of quark matter and the nature of compact objects.

Contribution

It introduces a two-zone interpolated hybrid EoS model and applies Bayesian analysis with multiple observational constraints to determine the properties of quark matter in neutron stars.

Findings

Quark matter phase must be color superconducting with specific coupling parameters.

Most probable solutions suggest a proportionality between diquark and vector couplings.

The analysis indicates the maximum mass of hybrid stars is below 2.5 solar masses.

Abstract

We introduce a family of equations of state (EoS) for hybrid neutron star (NS) matter that is obtained by a two-zone parabolic interpolation between a soft hadronic EoS at low densities and a set of stiff quark matter EoS at high densities within a finite region of chemical potentials $\mu_H < \mu < \mu_Q$. Fixing the hadronic EoS as the APR one and choosing the color-superconducting, nonlocal NJL model with two free parameters for the quark phase, we perform Bayesian analyses with this two-parameter family of hybrid EoS. Using three different sets of observational constraints that include the mass of PSR J0740+6620, the tidal deformability for GW170817, and the mass-radius relation for PSR J0030+0451 from NICER as obligatory (set 1), while set 2 uses the possible upper limit on the maximum mass from GW170817 as an additional constraint and set 3 instead of the possibility that the lighter object in the asymmetric binary merger GW190814 is a neutron star. We confirm that in any case, the quark matter phase has to be color superconducting with the dimensionless diquark coupling approximately fulfilling the Fierz relation $\eta_D=0.75$ and the most probable solutions exhibiting a proportionality between $\eta_D$ and $\eta_V$, the coupling of the repulsive vector interaction that is required for a sufficiently large maximum mass. We used the Bayesian analysis to investigate with the method of fictitious measurements the consequences of anticipating different radii for the massive $2~M_\odot$ PSR J0740+6220 for the most likely equation of state. With the actual outcome of the NICER radius measurement on PSR J0740+6220 we could conclude that for the most likely hybrid star EoS would not support a maximum mass as large as $2.5~M_\odot$ so that the event GW190814 was a binary black hole merger.